Focused charged particle beams are known and are in use in a variety of nanoscience and technology applications such as micromachining and nanofabrication of semiconductor chips. Typically, applicability of focused charged beams for a specific use depends upon parameters such as beam energy and diameter of the beams. It is often desirable to measure flux and beam profile of an impinging beam at a substrate to obtain information regarding an interaction region of the impinging beam on the substrate along with amount of energy being delivered through the beam. Many applications today use submicron and nanofocused ion beams. However, characterizing submicron and nanofocused beams, particularly measuring their spatial profiles is extremely difficult.
Techniques and equipment for focused beam measurement have been developed over some time. One way of characterizing the beams is direct beam profile measurement that involves analysis of craters formed on a substrate due to interaction of an impinging focused beam with the surface of the substrate. However, beam profile measurement using this technique can only be used to obtain profiles of low energy ion beams. Moreover, the substrate to be analyzed is required to be replaced after each exposure to the focused beam. In addition, the absolute value of beam currents cannot be determined using this technique and it is cumbersome to ascertain profile of the beam owing to erosion of the substrate.
Certain other systems use two-dimensional Faraday cup array placed in the beam path to measure the beam currents. A Faraday cup is a detector that measures the current in a focused charged beam and typically includes a metal cup or housing mounted on an insulator. An array of Faraday cups is placed in the path of the focused charged beam and an electrical lead is attached that conducts the current to a measuring device. Unfortunately, a large number of Faraday cups may be required to measure the beam currents due to a finite size of each cup. In addition, this technique is limited to characterization of beams with diameter greater than 1 mm.
Another measurement technique uses a wire scanner to measure the currents and the beam profile. The wire scanner includes a thin straight wire formed of a light material that is passed through the beam to measure the beam profile. Again, this technique cannot be used to characterize submicron and nanofocused ion beams because of limitations posed by the wire diameter of the scanner.